A simple circuit that is able to indicate if an injection‐locked oscillator is in the locked condition by providing a ‘high’ or ‘low’ output is presented. The detector is compatible with most injection‐locked oscillators as all that is required is access to the low‐frequency bias circuit, with no direct access needed to the RF/microwave signals. To prove the universal nature of the lock detector it is successfully demonstrated practically for two scenarios: (i) a 1 GHz injection‐locked VCO and (ii) a 60 GHz SiGe VCO MMIC.